Presently, most industrial diesel engines are equipped with mechanical injection devices. Most mechanical fuel injection devices use a piston type, mechanical pump which causes an injector nozzle valve to open under the increased pressure applied thereto. The fuel injection ends as the pressure drop allows the injector nozzle valve to return on its seat by means of a suitable return spring.
The beginning and the end of the fuel injection spray from the injector nozzles are, therefore, dependent upon the selective control of pressure in an hydraulic system, as well as upon the interaction of the injector nozzle valve return spring.
Such prior art mechanical fuel injection devices, known for their sturdiness and reliability, are, however, limited in their performance when an improved combustion is required. When using the prior art mechanical pumps, it is indeed difficult to accurately monitor and control the duration of an injection cycle and the fuel spray pressure.
In addition the accurate monitoring of the beginning or timing of the fuel injection spray cycle and the regulation of injected flow depends on engine speed, the ambient conditions, and the engine condition (coolant temperature for instance) which parmeters become very important with the prior art injection means.
The present invention is directed to a new fuel injection apparatus providing all injection monitoring devices that are not normally included in the prior art injection systems, or that are included therein at the cost of a greater complexity.
In the field of fuel injection, it is well known that fuel spray injector require the pressurization of fuel, as well as an electromechanical or hydraulically controlled slide valve so as to deliver the high pressure fuel to a fuel spray injector. In these prior art devices, only one controlled slide valve controls the beginning and the end of the fuel spray injection, and the occassionally flow regulation (by fuel controlling the opening duration).
In these known devices, the slide valve is fed by an electronic power station which operates according to the various parameters affecting the fuel spray injection. However, it is very difficult, if not impossible to control the timing off the start and the end of the fuel spray injection cycle as well as the regulation of the fuel flow, using a single slide valve, because of the great accuracy required in controlling these parameters during a very short period of time. It should be remembered that the fuel spray injection cycle duration on a truck diesel engine lasts about thirteen ten thousands of a second (0.0013) at full speed and about three thousands of a second (0.003) at a maximum torque. At full speed, the time period separating the start and end of the fuel spray injection is approximately five hundredths of a second (0.05). The required accuracy is then less than one tenth of a millisecond (0.1 msec) that is, roughly one sexagesimal degree of the rotation angle of the drive wheel or flywheel.